1. Field of the Invention
This invention relates to an illuminating apparatus, and particularly to an illuminating apparatus suitable for an optical apparatus having no surplus in the vertical thickness thereof and a photographing apparatus using the same, and is suitable for being mounted, for example, on a portion of the main body of a camera (the main body of a photographing apparatus), and operatively associated with the photographing operation of the main body of the camera to efficiently apply illuminating light (flashlight) to an object side and photograph the object.
2. Description of the Prior Art
Heretofore, an illuminating apparatus used in a photographing apparatus such as a camera has been comprised of a light source and optical parts such as a reflector and a Fresnel lens for forwardly directing a beam emitted from the light source.
In such an illuminating apparatus, various propositions have heretofore been made in order to cause beams emitted from the light source in various directions to be efficiently condensed within a necessary illuminating angle of view. Particularly in recent years, there has been proposed an illuminating apparatus in which an optical member utilizing total reflection such as a prism or a light guide is disposed instead of the Fresnel lens so far disposed in front of the light source, whereby an improvement in condensing efficiency and the thinning of an optical system in the vertical direction thereof are made compatible.
As a proposition of this kind, as shown in Japanese Patent Application Laid-Open No. 10-115852 by the applicant, there has been proposed an illuminating optical system using a compact prism of high condensing efficiency which causes a beam incident from a light source onto an optical member to be condensed in a vertical direction by total reflection surfaces formed on upper and lower sides and in a horizontal direction by a cylindrical lens surface provided on an emergence surface.
Also, as shown in Japanese Patent Application Laid-Open No. 11-249209, there has been proposed an illuminating optical system in which in order to prevent lateral stripe-shaped uneven light distribution caused by the above-described construction, there is disposed another optical member having a plurality of cylindrical lenses formed on the emergence surface side of the optical member.
In recent years, in a photographing apparatus such as a camera, the downsizing of the apparatus itself has been advancing more than heretofore. Particularly as a recent tendency, a desire to make the vertical height of the camera small is strong and along therewith, also for a strobo flash emitting portion located on the upper portion of the camera, a desire to reduce the vertical thickness thereof is strong. From such a background, it is strongly desired to put a thin type strobo optical system free of the deterioration of optical performance to practical use.
So, the applicant has proposed in Japanese Patent Application Laid-Open No. 10-115852 a thin type light emitting portion having its vertical thickness suppressed by utilizing a total reflection optical system which is little reduced in efficiency in spite of reflecting a plurality of times. This is an illuminating optical system of a thin type and good efficiency constructed by causing a beam incident from an illuminating light source onto an optical member to be condensed in a vertical direction (the diametral direction of a flashlight discharge tube) by total reflection surfaces formed on the upper and lower sides of the optical member to thereby achieve thinning, and to be efficiently condensed in a horizontal direction (the lengthwise direction of the flashlight discharge tube) by a cylindrical lens surface provided on the emergence surface of the optical member.
Referring to FIG. 11A of the accompanying drawings which is a schematic cross-sectional view of a flashlight emitting apparatus as such an illuminating apparatus, the reference numeral 2 designates a flashlight discharge tube such as a xenon tube having a light emitting source enclosed in a cylindrical glass tube, and the reference numeral 103 denotes a reflector, and the flashlight discharge tube 2 is mounted on the arcuate portion 103a thereof having an inner diameter shape substantially coinciding with the outer diameter shape of the flashlight discharge tube 2. This reflector 103 is such that the upper and lower reflecting surfaces 103b and 103b′ forwardly opening from the upper and lower ends of the arcuate portion 103a are formed into flat surfaces. The reference numeral 104 designates the above-described total reflection type optical member, and the incidence surface 104a thereof is disposed in the opening portion of the reflector 103, and the incident light of the flashlight discharge tube 2 emerges from a forward emergence surface 104b. Also, the upper and lower sides 104c and 104c′ of this optical member are formed into flat total reflection surfaces, and reflect a beam obliquely incident on the incidence surface 104a and causes it to emerge from the forward emergence surface 104b. 
On the other hand, as the evils of the thinning of the strobo optical system by the above-described method, there are the facts that the light distribution at a point of time whereat the light from the light source 2 is incident on the optical member 104 is non-uniform (the light is not uniformly incident on the whole of the incidence surface 104a of the optical member 104) and that in an actual product, space is limited and a sufficient length for uniformization cannot be secured, and therefore, as shown, for example, in FIGS. 11B to 11D of the accompanying drawings, beams painted in black become light portions and white portions among them become dark portions, and in each state, the total area of these light portions is not constant and thus, uneven light distribution on the irradiated surface has occurred. That is, the light portions and the dark portions have extended from left to right and have not been recognized as a plurality of lateral stripe-shaped uneven light distributions in which light portions and dark portions are formed alternately in a vertical direction.
As a remedy for this, as shown in Japanese Patent Application Laid-Open No. 11-249209, it has been proposed to adopt an illuminating optical system in which one more optical member formed with a plurality of cylindrical lenses is disposed on the emergence surface 104 side of the optical member 104, to thereby prevent uneven light distribution relatively efficiently without using a diffusing plate.
In this proposition for preventing lateral stripe-shaped uneven light distribution, however, the one more optical member is required and this has led not only to an increase in cost, but also to the necessity of an extra space in the longitudinal direction of the optical system.
Also, in terms of an optical characteristic, even a component which originally need not be diffused is changed and therefore, components outside the necessary illuminating angle range are somewhat produced, and the above-described remedy has not always been an efficient method of preventing uneven light distribution.
Also, the above-described prior art has lacked the consideration of effectively utilizing light spreading from left to right.
Also, related applications include U.S. Pat. Nos. 6,078,752, 6,467,931 and 6,400,905.